Electronic fueling governors for use with internal combustion engines are known and widely used in the automotive and diesel engine industries. In the heavy-duty diesel engine industry in particular, such governors typically include a reference speed logic circuit responsive to an accelerator pedal, hand throttle, cruise control or other signal indicative of a fueling request to produce a corresponding reference engine speed value. The reference engine speed value and a measured engine speed value, indicative of the actual rotational speed of the engine, are provided to a summation node where an error value indicative of a difference therebetween results. The error value is supplied to a controller that is configured to produce one or more fueling signals in a manner that minimizes the error value.
An electronic governor of the foregoing type has a number of operating parameters associated therewith that define the operational behavior of the governor. For example, the reference speed logic circuit defines a relationship between the operator requested fueling signal (i.e., accelerator pedal signal, hand throttle signal, cruise control fueling request signal or the like) and the reference engine speed value, wherein such an operator requested fueling signal will be referred to hereinafter as a “throttle signal.” In any case, this relationship between the throttle signal and the reference engine speed value typically includes a so-called “droop” value, wherein droop, in the context of the present invention, will be described with reference to FIG. 1.
Referring to FIG. 1, a plot 5 of engine output torque vs. engine speed is shown illustrating a torque curve 8 for an example heavy-duty diesel engine. The torque curve 8 defines an upper boundary of engine output torque/engine speed behavior, and accordingly represents a 100%, or full-load, fueling condition. In the context of the present invention, the term “engine output torque” will be used interchangeably with the term “fueling” such that 50% engine output torque is equivalent to 50% fueling, 100% engine output torque (corresponding to torque curve 8) is equivalent to 100%, or full-load fueling, etc. However, one caveat to these terms occurs at 0% engine output torque. It is generally understood that the engine may be running while producing no drive torque, and in this case, 0% engine output torque does not actually correspond to 0% fueling. Rather, under such conditions a certain minimum amount of fueling must be supplied to maintain the engine operational, and 0% engine output torque is typically referred to as a “no-load fueling” condition. For purposes of the subject invention, the term “no-load fueling” may thus be used interchangeably with 0% engine output torque.
Superimposed onto plot 5 is a first set of constant throttle values (e.g., 20% throttle, 40% throttle, etc.) identified as D1, wherein D1 represents a first droop value. Droop D1 is indicative of a so-called “min-max”, or “automotive”, governor defining throttle position as substantially proportional to engine output torque as illustrated in FIG. 1. Min-max governors of this type have heretofore been used in over-the-road truck applications and are generally characterized by flat droop lines as illustrated by D1. Another type of governor is a so-called “variable speed”, or “VS”, governor defining throttle position as substantially proportional to engine speed as illustrated by droop lines D2 in FIG. 1. VS governors of this type have heretofore been used in industrial machinery applications and are generally characterized by steep droop lines as illustrated by D2. In either case, droop is defined for purposes of the subject invention as an engine speed difference between full-load (torque curve) and no-load fueling (% engine output torque) for any constant throttle position. Thus, min-max governors (D1) have higher droop values as compared with VS governors (D2).
In over-the-road truck applications, it is generally understood that while min-max governors (D1) provide excellent tracking between throttle percentage and engine output torque, and are accordingly well-suited for low vehicle speed and vehicle launch conditions, they are generally ill-suited for smoothly maintaining engine speed during high vehicle speeds, during hilly terrain operation and with heavily loaded vehicles. Min-max governors are accordingly characterized as having optimal low vehicle speed/high transmission gear ratio response, but as having “slow pedal response” under high vehicle speed/low transmission gear ratio conditions. Conversely, while VS governors (D2) are generally understood to provide excellent tracking between throttle percentage and engine speed, and are accordingly well-suited for high vehicle speed, heavily loaded and hilly terrain operation, they are generally ill-suited for smoothly maintaining engine speed during slow vehicle speeds, over rough or bumpy roads and with lightly loaded vehicles. VS governors are accordingly characterized as having undesirably “fast pedal response” under low vehicle speed/high transmission gear ratio conditions, but as having optimal high vehicle speed/low transmission gear ratio response.
Due to the drawbacks associated with the two foregoing governor types, modern over-the-road trucks typically implement a so-called “hybrid” governor, illustrated in FIG. 1 by the dashed-lines of constant throttle percentage. Hybrid governors of this type are characterized by droop lines falling somewhere between the two droop extremes D1 and D2. It is generally understood that hybrid governors attempt, as a design goal, to capture an optimal mix between the min-max governor D1 and the VS governor D2. However, while such hybrid governors have been widely accepted, they do not capture the benefits of true min-max and VS governor behavior under operating conditions wherein such behavior would be desirable.
Another operating parameter associated with an electronic fueling governor that defines the operational behavior thereof is the overall gain of the governor controller. For purposes of the present invention, the overall gain of the governor controller is defined as the responsiveness of the governor to changes in the throttle signal to effectuate corresponding engine speed changes via control of the one or more fueling signals. Such overall controller gain is typically set in order to provide a desired governor responsiveness while also providing for controller stability.
What is needed is a fueling governor control system wherein governor behavior may be dynamically adjusted as a function of one or more engine and/or vehicle operating conditions to provide for VS and min-max governor behavior, and any hybrid governor behavior therebetween, when any such governor behavior is optimal for current engine/vehicle operating conditions.